Thanks for the kind words about the blog. I think you show a lot of potential and its a good sign that you're critical of your own work.

Few comments on your two dialogue tests. I really liked the subtext in your acting performances but I did find the mix of spline and stepped keys distracting.

(1) Dialogue 1:
(a) "mathletes"
This could be stronger - I would accent the dialogue by squinting the eyes on "m" and then popping them wide open. I expect to see the jaw open on "le" and close on "tes". On adding this I might rotate the head back up to support it.

(b) "queer"
I would like to see more intensity and frustration in the performace. You could try adding tension to the fingers with a stronger hand pose, and perhaps adding staggers to make her feel like she's boiling over.

(c) "I'm a pusher"
She's mimicing the girl with the intention of making her look and sound stupid, I would like to see a change in the way she moves to reflect this. I would suggest filming yourself as reference, and really play up the sarcasm. I would also go the other way with the facial expression, starting with a squint and then accenting the "p"s by widening the eyes.

(2) Dialogue 2:

Girl:
(a) I think she could be more anxious from the start - nervous finger drumming on the car door might help get this idea across, and even some eye darts towards him and then quickly looking away if there's time.
(b) As she kneels down her screen left hand needs more work - try spreading the fingers and/or adding a little push away from the door.
(c) Her expression in the last shot could be a more hopeful almost pleading one. I think there's enough time to add a little widening of the eyes and maybe a tightening of the lips as she awaits his answer with slight trepidation.

Guy:
(a) The connection of his elbow to his wrist sometimes feels too independent. I would expect to see the hand compensate for any translation in the elbow.
(b) Similarly have a look at the connection between his knee and ankle. I would expect to see the foot roll to compensate for a move in the knee.
(c) His left knee swims a little bit - it would be difficult to move when your weight is resting on it.
(d) When he looks from her back to the tyre, the timing of the chest, head and right arm needs to be broken up - they all hit the final pose at the same time.
(e) His lip synch seems underplayed - for example on "yeah yeah", I would like to see a tighter shape on "y" which broadens into "eah".

Regarding your polishing, in general, something you should concentrate a bit more is, the phyisics of your character, working more on how gravity affects his mass and the different parts of the body, also very important are the connections and the weight between those parts.
This is the main principle of "Force", why is that part stopping? How does it connects to the rest? What append to the character if this or that part is moving?